Randomization means that a participant is put into a group by chance (like flipping a coin). Neither the participant nor the research doctor will choose what group the participant will be in. Randomization will be 2:1 (twice as many of the participants in this study will receive mFOLFOX6+Ziv-aflibercept). This study is "blinded", which means neither the patient nor the doctor will know if the patient is getting the investigational drug or the placebo with the mFOLFOX6.